Smooth muscle relaxing drugs and guinea pig ileum.

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Abstract
The effects of various smooth muscle relaxing drugs on contractile responses to acetylcholine (ACh), Ba2+ and Ca2+, and on the tissue cAMP levels were examined in the guinea pig ileum. Papaverine and theophylline caused a decrease both in the maximum height and the slope of dose-response curves induced by the 3 stimulants, and an increase in the cAMP levels. Diltiazem and D-600 [methoxyverapamil] produced a decrease in the maximum and the slope of ACh and Ba2+ dose-response curves, shifted the Ca2+ dose-response curves to higher concentrations, in a parallel manner, but failed to change the cAMP levels. Etomidoline and benactyzine shifted the curves for the 3 stimulants in parallel to the right, but at higher concentrations depressed the maximum of ACh and Ba2+ responses with a further parallel shift. The drugs exerted little influence on the basal level of tissue cAMP, but etomidoline depressed the Ba2+-induced increase in cAMP level. The smooth muscle relaxing drugs used could be classified in 3 types, suggesting that there are at least 3 different mechanisms involved in smooth muscle relaxing action.